On both offshore and inland drilling barges and rigs, drill cuttings are conveyed up the hole by a drilling fluid. Water base drilling fluids may be suitable for drilling in certain types of formations; however, for proper drilling in other formations, it is desirable to use an oil base drilling fluid. With an oil base drilling fluid, the cuttings, besides ordinarily containing moisture, are necessarily coated with an adherent film or layer of oily drilling fluid which may penetrate into the interior of each cutting. This is true despite the use of various vibrating screens, mechanical separation devices and various chemical and washing techniques. Because of pollution to the environment, whether on water or land, the cuttings cannot be permanently discarded until the pollutants have been removed.
One method to accomplish the same has been placing the screen cuttings in a standpipe or other vessel filled with sea water and periodically skimming off the layer of displaced oil as it rises to the surface in the vessel. Another method tried was burning i.e. oxidatively incinerating the oil from the cuttings. Still another method was physically transporting the oily cuttings to a remote site for subsequent disposal. The standpipe method has proved in field trials not only inefficient, but actually compounds the initial pollution difficulties by generating large quantities of contaminated water, or solvents, which require separate treatment and disposal facilities apart from the original problem. The burning method presents risk of explosion and fire in connection with oil and gas drilling operations and inherent in the practice of a combustion disposal procedure. It is uniformally regarded by the drilling industry as well as by concerned safety regulatory agencies, as presenting too great a risk to be run even in association with elaborate fire prevention and control measures. The physical transportation method, while sometimes practical, and effective at the drilling location, requires establishment and maintenance of uninterrupted facilities for loading, unloading and transportation of the dirty cuttings, the operation of which presents in itself risks of environmental pollution, especially with offshore drilling sites. At the end of this chain of handling, an acceptable final disposal system must still be employed.
U.S. Pat. No. 3,693,951 to Lawhon et al, discloses a method of/and apparatus for the treatment of well cuttings especially adapted for offshore use. The apparatus of Lawhon et al comprises a heat resistant conveyor belt generally horizontally arranged so as to provide an input and a discharge end. A cuttings hopper is disposed above the input end for distributing well cuttings onto the conveyor belt where the agitating action of a vibrator serves to shake out water entrained in the cuttings. The conveyor belt then transports the cuttings to a heating chamber wherein the cuttings are subjected to infra-red radiation from the heating elements to drive off water from the face of the cuttings. Thereafter, the cuttings are transported on the conveyor belt through a heating and combustion chamber wherein they are subjected to high intensity infra-red radiation lamps and an air current which is drawn through a plenum of the combustion chamber. The air, along with the products of combustion, is vented by a blower through an exhaust duct. Following combustion of the entrained hydrocarbons, the cuttings are transported to the discharge end of the conveyor belt where they are sprayed with cooling water as they fall into a discharge hopper for disposal in the ocean.
U.S. Pat. No. 2,266,586 to Branum discloses apparatus for sampling oil well cuttings comprising a rotary conveyor element generally horizontally mounted in an open semi-cylindrical casing for receiving the well cuttings and conveying them to a discharge pipe at one end of the casing. As the cuttings are fed toward the discharge pipe, they are washed by the combined action of the water sprays above the casing and a fiber brush helically disposed on the conveyor element. A horizontal conveyor screw is arranged within an open trough mounted below the casing for receiving the washed cuttings and conveying them to the discharge pipe at one end of the trough. Disposed along the bottom of the trough is a gas burner for supplying heat to the trough to dry the cuttings as they are fed by the screw conveyor to the discharge pipe.
U.S. Pat. No. 3,658,015 to Griffin et al, discloses an explosive-proof method and incinerator for burning drill cuttings. The incinerator for removing hydrocarbon residues and other organic and inorganic components from oil and gas well drill cuttings is submerged in water to make the assembly explosive-proof with respect to the drilling rig. One embodiment uses a basket with a removable bottom in the combustion chamber to retain the cuttings during the burning. An alternate embodiment uses a series of metal plates for such retention. After burning, the pollution-free cuttings are discharged from the combustion chamber beneath the surface of the water to eliminate sparks which might otherwise also cause an explosion. A belt-driven scoop located beneath the combustion chamber provides a means of testing the burned cuttings for unburned pollutants.
U.S. Pat. No. 3,860,019 to Teague discloses an apparatus for avoiding water pollution at an offshore drilling site. The apparatus treats well drilling cuttings that normally accrue from the boring of a subterranean oil or gas well which process includes circulating a drilling mud. The cuttings are introduced to a preliminary separator for removing a major part of the drilling mud. Thereafter, while yet containing a minor portion of mud, cuttings are passed to a washer for contact with a cleaning detergent. A detergent recycling system simultaneously separates detergent from residue of the drilling mud, for reuse in the cutting cleaning process.
Accordingly, it is an object of the present invention to provide a safe means of treating oil or hydrocarbon coated or impregnated drill cuttings for disposal either on land or in a body of water, without incurring unacceptable environmental contamination or ecological upset.